1. Field of the Invention
The present invention relates to an imager. The imager includes a chip type, a package type, or a module type imaging device and a camera. In more particular, the present invention relates to a signal acquisition technique suitably applied, for example, to a solid-state imaging device using a semiconductor device capable of detecting and reading a physical value distribution in the form of electrical signals. In the above semiconductor device, unit constituent elements which have sensitivity to an electromagnetic wave, such as light or radioactive rays, input from the outside are arranged, and the physical value distribution is converted into the electrical signals by the unit constituent elements.
In particular, the present invention relates to the structure in which images of respective wavelength components are independently obtained, that is, for example, an image of a visible light component and an image of a wavelength component (such as infrared light) other than visible light are independently obtained.
2. Description of the Related Art
A semiconductor device for detecting a physical value distribution has been used in various fields, the semiconductor device having a plurality of unit constituent elements (such as pixels) arranged in lines or in a matrix, each of which has sensitivity to the change in physical value including electromagnetic waves, such as light or radioactive rays, input from the outside.
For example, in the filed of imaging apparatuses, a charge coupled device (CCD) type, a metal oxide semiconductor (MOS) type, and a complementary metal-oxide semiconductor (CMOS) type solid-state imaging device have been used for detecting the change in light (one type of electromagnetic wave) which is one example of a physical value. The devices read a physical value distribution in the form of electrical signals which are obtained through conversion of the above distribution by unit constituent elements (pixels in a solid-state imaging device).
For example, in a solid-state imaging device, photodiodes used as a photoelectric transducer (light-receiving element; photosensor) provided in an image-taking portion (pixel portion) of a device detect an electromagnetic wave, such as light or radioactive rays, input from the outside so as to generate and store signal charges, and the signal charges (photoelectrons) thus stored are read as image information.
In addition, in recent years, the structure for taking an image of visible light and an image of infrared light has been proposed (for example, see Japanese Unexamined Patent Application Publication Nos. 2004-103964, 10-210486, 2002-369049, 06-121325, 09-166493, 09-130678, and 2002-142228). For example, when a light-emitting point of infrared light is prepared beforehand and is then traced, the position of the light-emitting point of infrared light present in a visible image can be detected. In addition, even in the state in which visible light is not present such as in the night, when image-taking is performed while infrared light is irradiated, a clear image can be obtained. Furthermore, the sensitivity can be improved when infrared light is used in addition to visible light.
The structure described in Japanese Unexamined Patent Application Publication No. 2004-103964 is a single-plate system in which a visible image and an infrared image are separately obtained by exploiting the difference in position of light absorption in the depth direction of a semiconductor between wavelengths.
In addition, the structure described in Japanese Unexamined Patent Application Publication Nos. 10-210486, 2002-369049, and 06-121325 is a multiple plate system in which visible light and infrared light are separately received by respective imaging devices using a wavelength separation optical system such as a wavelength separation mirror or prism as an incident optical system.
For example, in Japanese Unexamined Patent Application Publication No. 10-210486, infrared light emitted from an infrared irradiation device is irradiated to an object, and at the same time, in an image-taking portion, an infrared component of light from the object is reflected on a cold mirror and is made incident on one sensor. In addition, a visible light component passing through the cold mirror is further separated into a red color component, a green color component, and a blue color component by three dichroic mirrors, and the above components are then made incident on respective sensors. The visible light side has the structure similar to that of a related three-plate system, that is, wavelength separation is performed in a wavelength region including R, G, and B colors to obtain respective sensitivities, so that an image is formed. As a result, three sensors are necessary and the cost is increased thereby; however, since the pixel size can be increased, the sensitivity can be improved.
In addition, in Japanese Unexamined Patent Application Publication No. 2002-369049, an iris diaphragm is provided for an image-taking lens system, an optical filter which only transmits light having a wavelength of approximately 770 to 950 nm (infrared wavelength region) is used as a blade of the iris diaphragm, and visible light and infrared light are further separated from each other by a dichroic mirror. In addition, an infrared-cut filter is provided at the transmitted visible light side, and a visible light-cut filter is provided at the reflected infrared light side. That is, after the wavelength separation is performed twice on a light path, the visible light and the infrared light are then made incident on respective sensors so as to separately obtain a visible image and an infrared image. The reason the diaphragm portion is formed to have a function of absorbing (or reflecting) infrared light is that the structure is formed to be used in three-dimensional measurement application.
In addition, the structure described in Japanese Unexamined Patent Application Publication No. 09-166493 is a single-plate system in which a rotary type wavelength separation optical system is used as an incident optical system and in which visible light and infrared light are received by the same imaging device. For example, in this structure, insertion and extraction of an infrared-cut filter is performed using a rotation mechanism, so that when the infrared-cut filter is inserted, a visible color image is output which is not influenced by near-infrared light and infrared light, and when the infrared-cut filter is extracted, an image is output which is obtained by adding the light intensity of visible light and that of near-infrared light.
In addition, the structure described in Japanese Unexamined Patent Application Publication No. 09-130678 is that visible light and infrared light are received by the same imaging device using a diaphragm optical system having a wavelength separation function as an incident optical system.
According to the structure described in Japanese Unexamined Patent Application Publication No. 2002-142228, four types of color filters each having its own filter characteristic are regularly provided for respective pixels of an imaging device having visible light and near-infrared light sensitivities, and matrix calculation of outputs of the pixels provided with the four types of color filters is performed, so that a visible color image and a near-infrared image can be independently obtained.